1. Field of the Invention
This invention relates to a surface potentiometer for measuring the surface potential of a conductor or an insulator in non-contact fashion. Particularly, it relates to a surface potentiometer suited for the measurement of the latent image potential on a photosensitive drum in an electrophotographic copying machine.
2. Description of the Prior Art
As a potentiometer of this non-contact type, there is a system of vibrating an electrode opposed to a surface to be measured and converting the potential into an AC signal, thereby measuring the potential of the surface to be measured, but such system must also employ a zero calibration system to provide a stable output and thus it is very much complicated in construction and in the arrangement of the detecting circuit. There is also a system whereby a chopper blade having a predetermined potential applied thereto is rotated between the surface to be measured and the measuring electrode to convert the potential into an AC signal, but this system has suffered from disadvantages such as production of great noise and difficulty with which the device is made compact.